Vertical insulated gate turn-off thyristor with intermediate p+ layer in p-base formed using epitaxial layer

A method for forming an insulated gate turn-off thyristor comprising:

• providing a first semiconductor layer of a first conductivity type;
• forming a second semiconductor layer of a second conductivity type over the first semiconductor layer;
• forming a third semiconductor layer of the first conductivity type over the second semiconductor layer;
• implanting dopants of the first conductivity type into a top surface of the third semiconductor layer;
• growing an epitaxial layer of the second conductivity type over the top surface of the third semiconductor layer;
• driving in the implanted dopants of the first conductivity type so that the dopants of the first conductivity type diffuse into the epitaxial layer of the second conductivity type and diffuse into the third semiconductor layer, wherein the diffused implanted dopants of the first conductivity type in the third semiconductor layer and the epitaxial layer form an intermediate portion of the first conductivity type having a dopant concentration at least 1.5 times the dopant concentration in the third semiconductor layer;
• forming a matrix of cells comprising a plurality of insulated gates within trenches formed within the epitaxial layer of the second conductivity type and the third semiconductor layer but not extending to the second semiconductor layer;
• and
• forming first regions of the second conductivity type in a top surface of the epitaxial layer of the second conductivity type, between the gates, wherein a vertical structure of npn and pnp transistors is formed, and conduction between the first semiconductor layer and the first regions of the second conductivity type is controlled by a voltage applied to the gates,
• wherein the gates are configured to form an inversion layer in the third semiconductor layer, when a certain potential is applied to the gates, to reduce an effective base width of one of the npn transistor or the pnp transistor to increase its beta to initiate regenerative thyristor action.